The fact that most snowmobiles are used over a multitude of surfaces makes it challenging to design them to be efficient in directional control on all surfaces. A significant advantage for a snowmobile would be if it enabled its driver to efficiently change direction on the varied surfaces it may encounter. The amount of effort and driving technique need can vary greatly between one surface to another as well as from one rider or snowmobile to another. Most snowmobiles turn well on groomed trails or hard packed snow surface with wider radius turns with minimal rider input. Often on trails and harder surfaces with tighter corners it is beneficial for riders to shift their weight to the inward side of the corner. Example, on a tight left hand corners the driver may find it beneficial to shift an appropriate portion of his body weight to left hand side of the snowmobiles. A properly proportioned weight shift helps to keep both skis and track in contact with the snow surface helping to guide the sled in a more controlled manner in the direction the rider has chosen. Driving snowmobiles in deeper snow can often require a more aggressive variation of the weight shifting technique than used for hard packed and groomed trails. The technique requires substantial amounts of physical movement and physical efforts from the rider to be effective while maneuvering over, through, up, down and around hills, trees and other obstacles in deeper snow.
Deeper snow riding techniques require a larger degree of weight shift and upper body strength combined with appropriate track thrust to initiate and maintain a lateral rolling motion of the snowmobile toward the inward side of a turn or the uphill or inward side of a slope. In executing a deeper snow riding technique turn the rider works to roll the chassis inward. In doing so the extension force of the outside ski spring will push the ski away from the chassis and often the ski will be in the air. At the same time the rider tries to overcome the inward ski's extension spring forces by a rider weight shift and pulling efforts toward the inward side, as a result the inward ski and its steering surfaces generally are in contact with the snow surface and the snowmobile rolls to the inward side when in deeper snow.
The basic deeper snow riding technique is illustrated in FIG. 1. The snowmobile chassis 10 has an inward side 12 and an outward side 14. The rider 16 has positioned a sizable amount of weight onto the inward side 12 which is nearest the uphill or inward side of the slope 18. The rider 16 is also pulling on the handlebar 20 toward the uphill or inward side. The effect of the rider's deeper snow technique on the snowmobile chassis 10 can be seen in that the outward ski 22 and outward control arm 26 are more extended away from the snowmobile chassis 10 than the inward ski 24 and inward control arm 28 which are compressed more toward the snowmobile chassis 10. The uphill or inward bottom edge of the track 30, acts to cut into the surface of slope 18, forming a ledge like surface that helps the snowmobile chassis 10 to hold its line while traversing slope 18.
The chassis' inward rolled position is largely the result of significant rider effort in executing the inward rider weight shift and the rider's pulling force which acts to overcome the inward ski spring's extension force. As a result of the chassis roll the track's bottom inside edge acts as a cutting edge that helps to cut a ledge like surface into the deeper snow and the snowmobile is able to hold a more controlled line while traversing across the slope of a hill or in a tighter turn than would otherwise be possible if the rider did not use this technique.
It is the inventors understanding that in deeper snow riding a ski suspension designed to reduce the amount of weight shift and pulling effort needed from the rider would help to affect more control in turns or slope traverses and would be advantageous.